This application claims the benefit of Korean Patent Application No. 1999-55107, filed on Dec. 6, 1999, under 35 U.S.C. xc2xa7119, the entirety of which is hereby incorporated by reference.
1. Field of the invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to a transflective LCD device.
2. Description of Related Art
In general, liquid crystal displays are divided into transmissive LCD devices and reflective LCD devices according to whether the display uses an internal or external light source.
A typical transmissive LCD device includes a liquid crystal panel and a back light device. The liquid crystal panel includes upper and lower substrates with a liquid crystal layer interposed. The upper substrate includes a color filter, and the lower substrate includes thin film transistors (TFTs) as switching elements. An upper polarizer is arranged on the liquid crystal panel, and a lower polarizer is arranged between the liquid crystal panel and the backlight device.
FIG. 1 is a partial perspective view of a transflective color LCD device.
A transflective LCD panel 11 comprises upper and lower substrates 15 and 21 opposing each other with liquid crystal 23 interposed. On the opposing surface of the upper substrate 15, color filters 17 having black matrix 16 and a transparent common electrode 13 are arranged sequentially.
The lower substrate 21 includes switching devices xe2x80x9cTxe2x80x9d and pixels xe2x80x9cPxe2x80x9d having pixel electrode 19 divided into transmissive portion 19a and reflective portion 19b. 
On the lower substrate 21, a plurality of gate and data lines 25 and 27 are positioned like an array matrix, and switching devices xe2x80x9cTxe2x80x9d is introduced into a matrix type.
An area defined by two adjacent gate and data lines 25 and 27 is the pixel xe2x80x9cPxe2x80x9d. On the pixel xe2x80x9cPxe2x80x9d, the transmissive portion 19a of the pixel electrode 19 can be composed of a transmitting hole or a transparent electrode. For the transmissive portion, the transparent electrode is conventionally employed.
Conductive metallic material having the superior reflectivity is used for the reflective electrode becoming the reflective portion 19a of the pixel electrode 19, and transparent conductive metallic material having the good transmissivity such as ITO (indium tin oxide) is used for the transparent electrode of the transmissive portion 19a. 
FIG. 2 is a cross-sectional view of the LCD device illustrating the operation principle of the transflective LCD device. As shown in FIG. 2, the conventional transflective LCD device 57 includes lower and upper substrates 43 and 53 with a liquid crystal layer 56 interposed there between. The upper substrate 43 has a color filter 17 (see FIG. 1), and the lower substrate 53 includes a switching device xe2x80x9cTxe2x80x9d (see FIG. 1), a transparent electrode 51 and a reflective electrode 49. The reflective electrode 49 is made of a conductive material having a good reflectivity and surrounds a transparent electrode 51 formed therein. The transflective LCD device 57 further includes a backlight device 41. The light transparent electrode 51 serves to transmit light xe2x80x9cAxe2x80x9d irradiated from the backlight device 41 and the reflective electrode 49 serves to reflect the ambient light xe2x80x9cBxe2x80x9d.
The transflective LCD device is operable in both a reflective mode and a transmissive mode. First, in the reflective mode, the ambient light xe2x80x9cBxe2x80x9d from the upper substrate 43 is reflected in the reflective electrode 49 and directs toward the upper substrate 43 again. At this time, when the electrical signals are applied to the pixel electrode (49 and 51) by the switching element xe2x80x9cTxe2x80x9d (see FIG. 1), phase of the liquid crystal layer 56 varies and thus the reflected light is colored by the color filter 17 (see FIG. 1) and displayed in the form of colored light.
Further, in the transmissive mode, light xe2x80x9cAxe2x80x9d generated from the backlight device 41 passes through the transparent electrode 51. At this time, when the electrical signals are applied to the pixel electrode (49 and 51) by the switching element xe2x80x9cTxe2x80x9d (see FIG. 1), phase of the liquid crystal layer 56 varies. Thus, the light xe2x80x9cAxe2x80x9d passing through the liquid crystal layer 56 is colored by the color filter 17 (see FIG. 1) and displayed in the form of images with other colored lights.
As described above, since the transflective LCD device has both the transmissive mode and the reflective mode, the transflective LCD device can be used without depending on the time of day (e.g., noon or dusk) and has advantages that it can be used for a long time with consuming a low power.
However, the efficiency of the light from the backlight device is lowered in the transmissive mode of the transflective LCD device.
FIG. 3 is a cross-sectional view of the conventional transflective LCD device.
An upper polarizer 45 is formed on the upper substrate 43, and the lower polarizer 47 and a retardation film 50 are formed sequentially under the lower substrate 53. Moreover, the upper and lower substrates 43 and 53 opposing each other with liquid crystal 55 interposed. On the opposing surface of the lower substrate 53, the reflective electrode 49 and the transparent electrode 51 are positioned.
Referring back to FIG. 1, an area defined by two adjacent gate and data lines 25 and 27 is the pixel xe2x80x9cPxe2x80x9d. On the pixel xe2x80x9cPxe2x80x9d, the pixel electrode 19 is comprised of the transmissive portion or transparent electrode 19a and the reflective portion or reflective electrode 19b. 
The LCD panel 57 having the upper substrate 43 and the lower substrate 53 divided into open region xe2x80x9cExe2x80x9d and closed region xe2x80x9cFxe2x80x9d depending on whether the light xe2x80x9cCxe2x80x9d and xe2x80x9cDxe2x80x9d generated from the backlight device 41 can be transmitted via the LCD panel 57. The closed region xe2x80x9cFxe2x80x9d includes the opaque metallic material such as the reflective electrode 49 of the pixel electrode, the gate line 25 and data line 27 (see FIG. 1). The open region xe2x80x9cExe2x80x9d includes the transparent electrode 51 of the pixel electrode.
In the transmissive mode, the light xe2x80x9cDxe2x80x9d generated from the backlight device 41 passes through the liquid crystal 55 and transparent electrode 51. However, the light xe2x80x9cCxe2x80x9d is absorbed by the lower polarizer 47 after being reflected in the reflective electrode 49, or a little of the light xe2x80x9cCxe2x80x9d passes through the liquid crystal 55.
FIG. 4 shows the state of light while it passes through each of the components described above.
The light generated from the backlight device 41 is first converted into linearly polarized light through the lower polarizer 47. The light, while passing through the lower polarizer 47, is absorbed except the parallel light to the transmitting axis of the lower polarizer 47. Therefore, the quantity of the light is being decreased.
The linearly polarized light is changed into left-circularly polarized light through the retardation film 50 having a phase difference xcex/4. Some of the left-circularly polarized light passes through the liquid crystal 55 (see FIG. 3) of the open portion xe2x80x9cExe2x80x9d, and the other of the left-circularly polarized light is reflected in the reflective electrode 49. At this time, the left-circularly polarized light is changed into the right-circularly polarized light due to the mirror effect. The right-circularly polarized light enters into the retardation film 50 again, and is converted into the linearly polarized light having a phase difference angle of 45 degrees.
That is, when the linearly polarized light enters into the lower polarizer 47, it is perpendicular to the transmitting axis of the lower polarizer 47. Therefore, the lower polarizer 47 absorbs most of the light.
As a result, the conventional transflective LCD device causes the decrease of the brightness since the closed portion xe2x80x9cFxe2x80x9d having the reflective electrode, gate line and data line absorbs the light.
Accordingly, the present invention is directed to a transflective liquid crystal display device that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the invention is to provide a transflective LCD device which can increase the brightness.
In accordance with the purpose of the invention, as embodied and broadly described, in one aspect the invention includes a transflective liquid crystal display device, including: upper and lower substrates opposing each other; a pixel electrode formed on the lower substrate and having reflective and transmitting portions; liquid crystal interposed between the upper substrate and the lower substrate; a backlight device providing light to the pixel electrode; and a reflective film for preventing the light from the backlight device from radiating to the reflective portion of the pixel electrode.
The transflective LCD device also has a lower polarizer under the lower substrate and the reflective film formed under the lower polarizer and having a transmitting hole corresponding to the transmitting portion of the pixel electrode. The area of the transmitting hole is smaller than that of the transmitting portion of the pixel electrode.
The lower substrate can be located under the reflective film and the lower polarizer. In the transflective LCD device, the reflective portion is made of the metallic material selected from a group composing of Aluminum, Tungsten, Molybdenum and the like. The transmitting portion is made of transparent conductive metallic material and can be replaced with a hole surrounded by the reflective portion.
In accordance with the purpose of the invention, in another aspect the invention provides a transflective liquid crystal display device, including: an upper substrate; an upper polarizer on the upper substrate; color filters under the upper substrate; a common electrode under the color filters; liquid crystal layer under the common electrode; a switching device under the liquid crystal; a pixel electrode, under the liquid crystal, having the transmitting and reflective portions and having an electrical connection with the switching device; a lower substrate under the pixel electrode; a lower polarizer under the lower substrate; a reflective film, under the lower polarizer, having a transmitting region; and a backlight device, under the reflective film, irradiating the light.
The transflective LCD device makes the light from the backlight pass through the transmitting region of the reflective film and transmit the transmitting portion of the pixel electrode. In the transflective LCD device, the area of the transmitting region for example a transmitting hole is smaller than that of the transmitting portion of the pixel electrode.
In accordance with the purpose of the invention, in another aspect the invention provides a transflective liquid crystal display device, including: an upper substrate; an upper retardation film on the upper substrate; an upper polarizer on the upper retardation film; color filters under the substrate; a common electrode under the color filters; liquid crystal layer under the common electrode; a switching device under the liquid crystal; a pixel electrode, under the liquid crystal, having the transmitting and reflective portions and having an electrical connection with the switching device; a lower retardation film under the pixel electrode; a lower polarizer under the lower retardation film; a reflective film, under the lower polarizer, having a transmitting region; a substrate under the reflective film; and a backlight device, under the lower substrate, irradiating the light.
The transflective LCD device makes the light from the backlight device pass through the transmitting region of the reflective film and transmit the transmitting portion of the pixel electrode into liquid crystal.